1. Field of the Invention
The present invention relates to an image-forming apparatus equipped with a neutralization light source for discharging electricity on an image carrier.
2. Related Art
A method that implements a second transfer of a toner image to a sheet is widely adopted for electrographic-type image-forming apparatuses. This method is known to form an electrostatic latent image by charging a photosensitive drum surface, which is an image carrier, and exposing the charged surface. Next, a so-called toner image is formed by attaching toner to the electrostatic latent image. In a primary transfer, that formed toner-image is transferred to an intermediate transfer belt. The secondary transfer involves transferring the toner-image on the intermediate transfer belt to a sheet of paper.
Tandem-type image-forming apparatuses, for example, have an intermediate transfer belt suspended between a drive roller and a driven roller. In order to form a toner-image on a surface of the suspended intermediate transfer belt, photosensitive drums of each color (magenta (M), cyan (C), yellow (Y), and black (Bk)) are disposed opposite primary transfer rollers sandwiching the intermediate transfer belt. With the image-forming method of this image-forming apparatus, first an exposure device forms an electrostatic latent image on a cylindrical surface of each photosensitive drum, then a developer develops that electrostatic latent image. Multiple layers of produced toner images are transferred (multi-layer transfer) to the intermediate transfer belt and that multi-layer toner-image formed on the intermediate transfer belt is finally transferred to a conveyed sheet of paper.
With this kind of image-forming apparatus, generation of transfer memory images, or exposure memory images sometimes is a problem.
For that reason, an image-forming apparatus was proposed that suppressed generation of transfer memory images, or exposure memory images by being equipped with neutralizing means for neutralizing electricity, further upstream than a cleaning device disposed further downstream than transfer positions.
However, with this kind of image-forming apparatus, toner images remained on the image carrier surface when transfer performance was inadequate; electrical discharge was sometimes inadequate where there was residual toner. In this kind of image-forming apparatus, exposure memory is sometimes generated.
Conversely, with this kind of image-forming apparatus, transfer performance is increased by setting a high transfer current. However, in such a case, different transfer currents flowing into the image carrier can affect image carrier charging characteristics. A problem of transfer memory occurs in this kind of image-forming apparatus.
In contrast, an image-forming apparatus has been proposed that irradiates a neutralization light onto an image carrier surface before a sheet passes through a transfer position of that image carrier; and via an optical system, a portion of that neutralization light irradiates to a separation position where printing paper that passes through the transfer position is separated from the photosensitive body, thereby facilitating the separation of the paper.
However, because one object of this kind of image-forming apparatus is to neutralize a charge to facilitate easy separation of the paper, the layout of the optical system is limited; it is difficult to save space. Still further, intensity of light irradiated onto the surface of the image carrier fluctuates depending on the type of paper and whether toner is present, because neutralization light is irradiated from a backside of the paper; sometimes uniform neutralization (discharging electricity) is not attained because of unstable neutralization.
It was proposed for another image-forming apparatus to dispose between a transfer position of an image carrier and a cleaning unit, a first neutralization light source for neutralizing residual electrical potential after a transfer, and to dispose between the cleaning unit and an electrical charging unit, a second neutralization light source using a lower light intensity than the first neutralization light source to neutralize electricity. This image-forming apparatus uses a second neutralization light source at a downstream side of the cleaning unit to neutralize residual electrical potential that is not adequately removed by the first neutralization light source to avoid the adverse effects residual electrical potential has on a subsequent image.
However, in a tandem-type image-forming apparatus, a photosensitive drum, which is an image carrier, is positioned adjacent to the developer and transfer belt. For that reason, disposing a pre-transfer neutralization light source is difficult; costs also rise because of an increase in the number of drive circuits associated with the second neutralization light source.